Sink float

Sink-float plants are usually custom-designed for each individual apphcation. However, for coal beneficiation modular units are avah-... 

The response of any given feed to sink-float processing can be accurately established in the laboratory by testing with various heavy hq-uids. The hquids generally used for this purpose are listed in Table 19-12. These halogenated hydrocarbons are mutually miscible, which enables the preparation of almost any pulp density attainable in a commercial plant. Heavy-hquid test work provides the basis for specifying the optimum screen size for the preparation of the feed. 

Chemical Additives The use of chemical additives in sink-float processing is not common except for the use of lime to prevent oxidation and decomposition of the medium. A small amount of clay is sometimes added to improve the kinetic stability of the suspension. 

Costs Because sink-float processing is applied to relatively coarse particles and is a single-pass operation, capital and operating costs are usually considerably lower than would be required for a flotation or a gravity mill of the same capacity. A large flow of water is required for feed preparation and for media recovery, but almost total recoveiy for recirculation is possible. A minimum of two job-trained operators per shift is generally required by law, but these would be able to attend several separators at almost any feed rate. 

To size the two species however, it is necessary to separate them. A sink-float technique has been developed to separate the two. A carbon tetrachloride - tetrabromoethane mixture having an SG about 2.5 was used. The dry crystal mixture is added to the dense organic liquid, then put under vacuum to remove entrapped air bubbles. The suspension is then centrifuged for several hours to separate out the gypsum which floats and the hemihydrate which sinks. Tests on synthetic mixtures showed that a very clean separation is possible. 

A sink-float technique has been developed for separating hemlhydrate from gypsum crystals for samples from mixed species crystallizers. 

Examples of mixed post-consumer plastic waste by the combination of a three-stage sink-float method and selective flotation have been presented. The appropriate conditions, e.g., wetting agents, frother, depressant, and pH condition, are of importance (122). 

S. Pongstabodee, N. Kunachitpimol, and S. Damronglerd, Combination of three-stage sink-float method and selective flotation technique for separation of mixed post-consumer plastic waste, Waste Manage. (Oxford), 28(3) 475—483,2008. 

Two trace element studies are being done to answer some of these questions. The first study, funded by the Environmental Protection Agency, concerns coal washing and is designed to determine the distribution of certain trace elements in coal. The various specific gravity fractions of coal are separated by a sink-float procedure. Commercially available organic fluids are used as the separation media. 

The mineral matter in the coke was extremely difficult to identify because it was finely disseminated throughout. X-ray diffraction techniques were used to gain some insight into the mineral content of the coke. In order to obtain x-ray diffraction patterns of the mineral matter, the interference of carbon had to be reduced to a minimum this was accomplished by grinding the coke to —200 mesh, sink-floating it in a 2.30-specific gravity liquid, and centrifuging. 

Particle size — 4% below 20 y Crystal density (sink-float) — 1.93g/cc... 

Determination of the washability characteristics of coal by the float and sink (float-sink) method can be applied to coal of any particle size provided suitably large vessels to hold the larger lumps are available. Air-dried coal, not dry coal, should be used since the separation depends partly on the difference in specific gravity of the clean coal and dirt particles, and the specific gravity, in turn, is dependent on the moisture content of the coal. If the coal is dried before the test is carried out, the conditions will then differ from those in commercial washers, and the results will be at variance with those obtained in practice. 

Preparative II DGC in Figure 1 is a scaled-up version of Preparative I which uses a combination of the sink-float separations followed by non-linear density gradient separation. With this technique 20-25 g of a maceral concentrate can be separated. In effect, for a three-fold increase in time for separation, isolation, and characterization, we obtain at least a ten-fold increase in the yield of maceral materials. 

Samples. Two of the coals used 1n this study were obtained from the Penn State Coal Sample Bank, an HVA bituminous coal (PSOC 1103) from the Upper Elkhorn 3 seam in Eastern Kentucky and an HVA bituminous coal (PSOC 828) from the Brazil Block seam in Indiana. A third coal from which vitrinite and fusinite were hand picked was an Illinois No. 2 seam HVC bituminous coal from Northern Illinois. Also, resinite and vitrinite samples were hand picked from a Hiawatha seam bituminous coal from the King 6 mine in Utah. Finally, the alginite sample was obtained from an Ohio No. 5 seam (PSOC-297) coal by 06C (2,5). All of the elemental and petrographic analyses are presented in Table I. The details of the sink-float technique have been reported previously (1). Typically, a 3 micron particle size demineralized coal Ts centrifuged in aqueous CsCl2 solution of the appropriate density with a small amount of surfactant added to disperse the coal particles. The exinites in the float are... 

See text for further description of the source of the samples, all elemental analyses on a dmmf basis SF = sink-float HP hand-picked and DGC = density gradient centrifugation 3%S + %0... 

Float-Sink or Suspension Method This method involves placing a solid sample into a liquid with known and adjustable density. The density of liquid is incrementally adjusted until the sample begins to sink-float (ASTM C729-75 [25]), or is suspended at neutral density in the liquid (ASTM C693-93 [26]). At the point of equilibrium the density of the sample is equal to the density of the liquid. 

ASTM C729-75 el (1995), Standard Test Method for Density of Glass by the Sink-Float Comparator, American Society for Testing and Materials, Philadelphia, PA. 

Birefringence measurements were obtained by the Becke line method, and density measurements were obtained by the sink-float method (26). 

Commercially deactivated FCC Beats of varying matrix types and containing a wide range of sodium were characterized by t-plot surface area (ASTM D4365-85) to determine the effect of Na on zeolite and matrix area stability. The Beats were also examined by electron microprobe (Cameca SX50) to determine the Na distribution within a catalyst particle. Some of the Beats were separated into eight age fractions based on a modified sink/float procedure described in the literature (13,14). Bach age fraction was analyzed by ICP, t-plot and zeolite unit cell size (ASTM D3942-91). 

Catalyst and trap blends were steamed in a fluid bed using the same conditions as in Table I. Weight blend ratios with 95/5, 90/10, 85/15 of catalyst trap for both the fine and the coarse fractions were steamed, and the sink/float technique was again used to measure the rate of vanadium transfer. The results (Table III) show that there is not a strong dependence of the vanadium transfer rate on particle size. The rate enhancement, which is the rate of the fine catalyst / rate of the coarse catalyst, only varies by 10%, whereas the number density varied by a factor of 6.5. This experiment shows that the rate of vanadium transfer from catalyst to trap is only weakly dependent on the particle density, and it implies that particle-to-particle collisions are not the dominant mode of vanadium transfer. 

---